Genomic basis of phenotypic variability of complex disorders Abstract Recent studies have suggested a class of rare CNVs that are often inherited as well as associated with various complex disorders including intellectual disability, congenital cardiac disease, obesity, epilepsy, autism, and schizophrenia. While these CNVs confer a higher risk for disease, they are not necessarily sufficient to cause disease. This implies a need to consider additional genetic factors that may account for phenotypic variability. Our long-term interests are to understand how a combination of genetic variants can lead to specific clinical outcomes. The specific aims proposed will help us to identify all forms of genetic variants in individuals with 16p12.1 deletion and to understand the biological mechanisms for variability from functional studies in model systems. Our three specific aims are to: (1) Perform whole genome sequencing (WGS) of 100 families, including an estimated 325 individuals (75 trios and 25 quad families), with at least one affected individual carrying a 16p12.1 deletion, to identify copy-number variants (CNVs), single nucleotide variants (SNVs), and insertion-deletions (INDELs) using a combination of variant-detection algorithms; (2) Prioritize genetic variants for disease and functional association,, perform quantitative phenotyping of families with 16p12.1 deletion, and integrate genetic data with phenotypic data to identify specific patterns of genetic variants contributing to the observed traits; (3) Perform functional studies in model systems to test dosage-sensitivity of Drosophila melanogaster and Xenopus leavis orthologs of 16p12.1 genes using highly sensitive quantitative methods, and assess the effect of a selected ten candidate modifier genes by two locus models. This proposal will aid in identifying biologically valid variants that interact with 16p12.1 genes contributing towards specific phenotypes, which will help in a more accurate diagnosis of specific subtypes of developmental disorders, and provide impetus for targeted treatment strategies.